"After a period of less activity, we can expect a gradual increase in attacks by the Informal Anarchist Federation (FAI)," Giorgio Piccirillo told the Italian parliaments' constitutional affairs committee in Rome.
The previously unknown 'Olga' cell of the FAI claimed the shooting in the leg of Italian nuclear company Ansaldo's boss Roberto Adinolfi in the northwestern port city of Genoa earlier in May.
The FAI was also becoming better organised and was probably gaining more members although its lack of structure made it hard to assess its strength, Piccirillo said.
"They are like gas, you don't realise when it's expanding, only when it explodes," he stated.
While the FAI was currently the main anarchist group active in Italy, further attacks and threats by unknown groups were likely, Piccirillo warned.
"There may be attacks by hitherto unknown groups and we can expect an increase in threats inspired by the Years of Lead," he said, referring to the politically motivated violence that raged in Italy during the 1970s and 1980s.
Targets were like to include security forces, companies and banks, power plants and tax agencies, he said.
The threat posed by far-left groups must also "be considered," according to Piccirillo, warning these groups could exploit anger at the recession and government fiscal austerity to seek new recruits to their cause..
Four leaflets signed by Italy's Marxist-Lenninist Red Brigades were left on 11 May in several locations in Legnano, near Milan, including tax collection offices and the national pension and insurance fund INPS.
The Marxist-Lenninist group last week threatened to assassinate Giuseppe Orsi, the chief of Italian aerospace and defence giant Finmecchanica of which Ansaldo is a part.
Earlier this month, Italy's interior minister Annamaria Cancellieri said the government had ordered relevant agencies to raise the terrorism alert level at sensitive sites and said Italian soldiers could be stationed at these sites to protect them.